Classes and

Data Abstraction

Topic 5

Introduction

Object-oriented programming (OOP)

– Encapsulates data (attributes) and functions

(behavior) into packages called classes

– The data and functions of a class are intimately

tied together.

– A class is like a blue Print,

– With the help of blue print builder can make a

house, out of a class a programmer can create

an object.

Introduction

– One blue print can be reused many times to

make many houses, similarly one class can be

reused many times to make many objects of the

same class.

– Procedural language programming tends to be

action oriented, c++ programming is object

oriented.

– The unit of the programming in c is the

function where in C++ is the class

– Classes are also referred to as programmer

defined types.

Introduction

– Each class contains data as well as the set of functions that manipulate the data.

– The data components of a class are called data members. The function components of a class are called member function.

Information hiding

– Class objects communicate across well-defined interfaces

– Implementation details hidden within classes themselves

User-defined (programmer-defined) types: classes

– Data (data members)

– Functions (member functions or methods)

– Similar to blueprints – reusable

– Class instance: object

What are Classes?

Class

Data

Operations

Object

Data

Operations

Object

Data

Operations

Object

What are Classes? Class

User Defined Data Type

Data Value

Operations Member Functions

Object Variable

Data Value

Operations Member Functions

Object Variable

Data Value

Operations Member Functions

Object Variable

What are Classes?

A class is a data type

You can use classes in the same way you

use predefined data types (int, char, etc.)

Defining your class the right way is

important for it to behave like predefined

data types Abstract Data Type (ADT)

An ADT is a user-defined data type that is

well behaved as the predefined data types

Structures

A data structure that can be used to store

related data items with different types.

The individual components of a struct is

called a member.

Structures

Student

– ID

– Name

– Major

ID Name Major

1111 Nora CS

2222 Sara IS

3333 Mona CS

Students

Student: ID variable

Student: Name variable

Student: Major variable

Structures

Think of a structure as an object without any

member functions

Data Value

Operations Member Functions

Object Variable

Here, we’ll have values of different

data types that we would like to

treat as a single item.

Structures

How do I….

– Define a structure?

– Use a structure?

Student

ID

Name

Major

struct Student { int id; char name[10]; char major[2]; };

Structures

Syntax: struct Structure_Tag

{

Type1 Member_Variable1;

Type2 Member_Variable2;

Typen Member_Variablen;

};

Structures

Using Structures

– Declare:

StudentRecord Student1, Student2;

– Assignment: Student1 = Student2;

• Student1.id = Student2.id;

• Student1.grade = Student2.grade;

– Read: cin >> Student1.id;

– Write: cout << Student1.id;

– Initialize: Student1 = {666,’A’}

Structures

Syntax: Structure_Variable_Name.Member_Variable_Name

Example:

struct StudentRecord

{

int id;

char grade;

};

int main ()

{

StudentRecord Student1;

Student1.id = 555;

Student1.grade = ‘B’;

cout<< Student1.id<< ‘, ‘<< Student1.grade<<endl;

}

Dot Operator

Structures

Two or more structure types may use the same member

names

struct FertilizerStock

{

double quantity;

double nitrogen_content;

};

struct CropYield

{

int quantity;

double size;

};

FertilizerStock Item1;

CropYield Apples;

Apples.quantity

Item1.quantity

Structures

Structures within structures (nested)

struct Date

{

int month;

int day;

int year;

};

struct Employee

{

int id;

Date birthday;

};

Employee person1;

cout<< person1.birthday.year;

Structures #include <iostream>

struct StudentRecord

{ int id;

char grade;

};

StudentRecord Get_Data (StudentRecord in_student);

int main ()

{ using namespace std;

StudentRecord Student1;

Student1 = Get_Data (Student1);

cout<< Student1.id<< ","<<Student1.grade<< endl;

return 0;

}

StudentRecord Get_Data (StudentRecord in_student)

{ using namespace std;

cout<<"Enter ID: "; cin>> in_student.id;

cout<<"Enter Grade: "; cin>> in_student.grade;

return (in_student);

}

fig06_01.cpp

(1 of 3)

1 // Fig. 6.1: fig06_01.cpp

2 // Create a structure, set its members, and print it.

3 #include <iostream>

4

5 using std::cout;

6 using std::endl;

7

8 #include <iomanip>

9

10 using std::setfill;

11 using std::setw;

12

13 // structure definition

14 struct Time {

15 int hour; // 0-23 (24-hour clock format)

16 int minute; // 0-59

17 int second; // 0-59

18

19 }; // end struct Time

20

21 void printUniversal( const Time & ); // prototype

22 void printStandard( const Time & ); // prototype

23

Define structure type Time

with three integer members.

Pass references to constant Time objects to eliminate

copying overhead.

fig06_01.cpp

(2 of 3)

24 int main()

25 {

26 Time dinnerTime; // variable of new type Time

27

28 dinnerTime.hour = 18; // set hour member of dinnerTime

29 dinnerTime.minute = 30; // set minute member of dinnerTime

30 dinnerTime.second = 0; // set second member of dinnerTime

31

32 cout << "Dinner will be held at ";

33 printUniversal( dinnerTime );

34 cout << " universal time,\nwhich is ";

35 printStandard( dinnerTime );

36 cout << " standard time.\n";

37

38 dinnerTime.hour = 29; // set hour to invalid value

39 dinnerTime.minute = 73; // set minute to invalid value

40

41 cout << "\nTime with invalid values: ";

42 printUniversal( dinnerTime );

43 cout << endl;

44

45 return 0;

46

47 } // end main

48

Use dot operator to initialize

structure members.

Direct access to data allows

assignment of bad values.

fig06_01.cpp

(3 of 3)

fig06_01.cpp

output (1 of 1)

49 // print time in universal-time format

50 void printUniversal( const Time &t )

51 {

52 cout << setfill( '0' ) << setw( 2 ) << t.hour << ":"

53 << setw( 2 ) << t.minute << ":"

54 << setw( 2 ) << t.second;

55

56 } // end function printUniversal

57

58 // print time in standard-time format

59 void printStandard( const Time &t )

60 {

61 cout << ( ( t.hour == 0 || t.hour == 12 ) ?

62 12 : t.hour % 12 ) << ":" << setfill( '0' )

63 << setw( 2 ) << t.minute << ":"

64 << setw( 2 ) << t.second

65 << ( t.hour < 12 ? " AM" : " PM" );

66

67 } // end function printStandard

Dinner will be held at 18:30:00 universal time,

which is 6:30:00 PM standard time.

Time with invalid values: 29:73:00

Use parameterized stream

manipulator setfill.

Use dot operator to access

data members.